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Section 1: Harvesting and preparation for market


Maturity standards
Harvesting practices
Harvesting containers
Harvesting tools
Field packing
Transport to the packinghouse

Mechanical damage during harvest can become a serious problem, as injuries predispose produce to decay, increased water loss and increased respiratory and ethylene production rates leading to quick deterioration. In general, harvesting by machine will cause more damage than harvesting by hand, although some root crops can be severely damaged by careless hand digging. The containers used by pickers in the field should be clean, have smooth inside surfaces and be free of rough edges. Stackable plastic crates, while initially expensive, are durable, reusable and easily cleaned (FAO, 1989). If baskets are used, they should be woven "inside out" with the stubs of the beginning and end of each cane on the outside of the basket (Grierson, 1987).

Manual harvesters should be well trained in the proper way to harvest the crop to minimize damage and waste, and should be able to recognize the proper maturity stage for the produce they are handling. Pickers should harvest with care, by snapping, cutting or pulling the fruit or vegetable from the plant in the least damaging manner. The tips of knives should be rounded to minimize inadvertent gouges and excess damage to perennial plants. Knives and clippers should always be well sharpened. Pickers should be trained to empty their picking bags and/or baskets with care, never dumping or throwing produce into field containers. If harvesters pick directly into large bulk bins, produce can be protected from bruising by the use of a deaccelerating chute fashioned from canvas. Vented, stackable field containers should be kept clean and smooth.

Exposure to the sun should be avoided as much as possible during and after harvest, as produce left out in the sun will gain heat and may become sun-burned. Field bins should be placed in the shade or loosely covered (for example with light colored canvas, leafy plant materials, straw or an inverted empty container) if delays are expected in removing them from the field. Night or early morning harvest is sometimes an option for harvesting produce when internal temperatures are relatively low, reducing the energy needed for subsequent cooling. Latex flow is often lower later in the morning than it is at dawn for crops such as mango and citrus (Pantastico, 1980), so harvesting as late in the morning as possible can also reduce later efforts required to clean the produce before packing.

Directly following harvest, when produce is prepared for marketing, cooling is essential. Cooling (also known as "pre-cooling") is the removal of field heat directly after harvest, before any further handling. Any delays in cooling will shorten postharvest life and reduce quality. Even produce undergoing repeated cooling and warming deteriorates at a slower rate than produce that has not been cooled (Mitchell et al, 1972).

Rough handling during preparation for market will increase bruising and mechanical damage and limit the benefits of cooling. Roads between the field and the packinghouse should be graded and free from large ruts, bumps and holes. Field boxes must be well-secured during transport and, if stacked, not overfilled. Transport speeds must be suited to the quality and conditions of the roads, and truck and/or trailer suspensions kept in good repair. Reduced tire air pressure on transport vehicles will reduce the amount of motion transmitted to the produce (Mitchell in Kader, 1992).

Any practice that reduces the number of times the produce is handled will help reduce losses. Field packing (selection, sorting, trimming and packaging of produce at the time of harvest) can greatly reduce the number of handling steps the produce must undergo before marketing. Small, mobile field packing stations can be designed to be moved along with the packers and to provide shade for packing operations.

Maturity standards

Maturity standards have been determined for many fruit, vegetable and floral crops. Harvesting crops at the proper maturity allows handlers to begin their work with the best possible quality produce. Produce harvested too early may lack flavor and may not ripen properly, while produce harvested too late may be fibrous or overripe. Pickers can be trained in methods of identifying produce that is ready for harvest. The following table, from Reid (in Kader, 1992) provides some examples of maturity indices.

Index

Examples

Elapsed days from full bloom to harvest

Apples, pears

Mean heat units during development

Peas, apples, sweet corn

Development of abscission layer

Some melons, apples, feijoas

Surface morphology and structure

Cuticle formation on grapes, tomatoes
Netting of some melons
Gloss of some fruits (development of wax)

Size

All fruits and many vegetables

Specific gravity

Cherries, watermelons, potatoes

Shape

Angularity of banana fingers
Full cheeks of mangos
Compactness of broccoli and cauliflower

Solidity

Lettuce, cabbage, brussels sprouts

Textural properties

Firmness

Apples, pears, stone fruits

Tenderness

Peas

Color, external

All fruits and most vegetables

Internal color and structure

Formation of jelly-like material in tomato fruits
Flesh color of some fruits

Compositional factors

Starch content

Apples, pears

Sugar content

Apples, pears, stone fruits, grapes

Acid content, sugar/acid ratio

Pomegranates, citrus, papaya, melons, kiwifruit

Juice content

Citrus fruits

Oil content

Avocados

Astringency (tannin content)

Persimmons, dates

Internal ethylene concentration

Apples, pears

Source: Kader, A. A. 1983. Postharvest Quality Maintenance of Fruits and Vegetables in Developing Countries. In: Lieberman, M., Post-Harvest Physiology and Crop Preservation. Plenum Publishing Corporation. p.455-469.

Vegetables are harvested over a wide range of maturities, depending upon the part of the plant used as food. The following table provides some examples of maturity indices of vegetable crops.

Crop

Index

Root, bulb and tuber crops

Radish and carrot

Large enough and crispy (overmature if pithy)

Potato, onion, and garlic

Tops beginning to dry out and topple down

Yam bean and ginger

Large enough (overmature if tough and fibrous)

Green onion

Leaves at their broadest and longest

Fruit vegetables

Cowpea, yard-long bean, snap bean, batao, sweet pea, and winged bean

Well-filled pods that snap readily

Lima bean and pigeon pea

Well-filled pods that are beginning to lose their greenness

Okra

Desirable size reached and the tips of which can be snapped readily

Upo, snake gourd, and dishrag gourd

Desirable size reached and thumbnail can still penetrate flesh readily (overmature if thumbnail cannot penetrate flesh readily)

Eggplant, bitter gourd, chayote or slicing cucumber

Desirable size reached but still tender (overmature if color dulls or changes and seeds are tough)

Sweet corn

Exudes milky sap when thumbnail penetrates kernel

Tomato

Seeds slipping when fruit is cut, or green color turning pink

Sweet pepper

Deep green color turning dull or red

Muskmelon

Easily separated from vine with a slight twist leaving clean cavity

Honeydew melon

Change in fruit color from a slight greenish white to cream; aroma noticeable

Watermelon

Color of lower part turning creamy yelow, dull hollow sound when thumped

Flower vegetables

Cauliflower

Curd compact (overmature if flower cluster elongates and become loose)

Broccoli

Bud cluster compact (overmature if loose)

Leafy vegetables

Lettuce

Big enough before flowering

Cabbage

Head compact (overmature if head cracks)

Celery

Big enough before it becomes pithy

Source: Bautista, O.K. and Mabesa, R.C. (Eds). 1977. Vegetable Production. University of the Philippines at Los Banos.

Harvesting practices

Harvesting practices should cause as little mechanical damage to produce as possible. Gentle digging, picking and handling will help reduce crop losses.

Pick carefully to avoid damage:

For some crops, a natural break point forms at the junction of the stem and the stalk when produce is mature. Harvesters should grasp the product firmly but gently and pull upward as illustrated below. Wearing cotton gloves, trimming fingernails, and removing jewelry such as rings and bracelets can help reduce mechanical damage during harvest.

Source: FAO. 1989. Prevention of Post-Harvest Food Losses: Fruits. Vegetables and Root Crops. A Training Manual. Rome: UNFAO. 157 pp.

If a small amount of leafy vegetables are being harvested for home use or for sale at a nearby roadside or farmers' market, a small tub of cold water can be useful for cooling the produce. The tub can be brought directly to the field and used by the picker as a field container. Clean water should be used with each lot of produce. Chilling leafy vegetables by using cold water at harvest will help maintain quality and prevent wilting.

Source: Minnich, J. 1983. Gardening for Maximum Nutrition. Emmaus, Pa: Rodale Press.

Harvesting containers

Picking baskets, bags and buckets come in many sues and shapes. These harvesting containers can be made by sewing bags with openings on both ends, fitting fabric over the open bottom of ready-made baskets, fitting bags with adjustable harnesses, or by simply adding some carrying straps to a small basket. Several examples are illustrated below.

Source: Friend Manufacturing Corporation, Prospect Street, P.O. Box 385, Gasport, New York 14067

Plastic crates are relatively expensive but are durable, reusable and easy to clean. When empty, they can be nested to save space in storage or transport. When filled they can be stacked if every other crate is turned in the direction opposite to the one below.

Stackable, reusable plastic crates:

Source: FAO. 1989. Prevention of Post-Harvest Food Losses: Fruits, Vegetables and Root Crops. A Training Manual. Rome: UNFAO. 157 Pp.

Harvesting tools

Some fruits need to be clipped or cut from the parent plant. Clippers or knives should be kept well sharpened. Penduncles, woody stems or spurs should be trimmed as close as possible to prevent fruit from damaging neighboring fruits during transport.

Pruning shears are often used for harvesting fruits, some vegetables, and cut flowers. A variety of styles are available as hand held or pole models, including shears that cut and hold onto the stem of the cut product. This feature allows the picker to harvest without a catching bag and without dropping fruits.

Straight bladed hand shears for fruits and flowers:

Thin curved blade for grapes and fruits:

Cut and hold hand shears:

Clipper for citrus fruits:

Pole mounted cut and hold picking shears:

Sources: See Appendix A for suppliers of harvesting tools.

Using a cutting tool attached to a long pole can aid picking of crops such as mangoes and avocados when the fruit is difficult to reach. Cutting edges should be kept sharpened and the catching bag should be relatively small The angle of the cutting edge and the shape of the catching bag can affect the quality of the fruit harvested, so it is important to check performance carefully before using any new tools.

Using a picking pole:

Picking poles and catching sacks can be made by hand or purchased from horticultural supply companies. The collection bags illustrated below were hand woven from strong cord or sewn from canvas. The hoop used as the basket rim and cutting edges can be fashioned from sheet metal, steel tubing or recycled scrap metal.

Hand woven collection bag

Canvas collection sack

Fruit trees are sometimes quite tall and letting fruit fall to the ground when it is cut from the tree will cause severe bruising. If two pickers work together, one can clip or cut the fruit from the tree, and the other can use a sack to break its fall. The catcher supports the bag with his hands and one foot, catches the falling fruit, then lowers the far end of the bag to allow the fruit to roll safely to the ground.

Source: FAO. 1989. Prevention of Post-Harvest Food Losses: Fruits. Vegetables and Root Crops. A Training Manual. Rome: UNFAO. 157 pp.

Unlike most nut crops, pistachio nuts should not be knocked to the ground during harvest because of their open shells and relatively high moisture content. The harvesting practice illustrated below can be used with pistachios and olives with good results. Plastic sheeting or canvas tarpaulins are spread below the tree being harvested, and trees are mechanically shaken or hand knocked (the branches hit with mauls) until the nuts drop. In the illustration below, two harvesters are gathering a sheet covered with produce.

Field packing

When crops are field packed the picker harvests and then immediately packs the produce after minimal handling Strawberries are generally field packed, since even a small amount of handling will damage these soft fruits. When lettuce is field packed, several wrapper leaves are left on the head to help cushion the produce during transport.

A small cart can help reduce the amount of bending and lifting the picker has to do during harvest. The carts shown below have a single wheel in front, and can be pushed along the row ahead the e picker.

Field packing strawberries:

Field packing lettuce:

A simple aid for field packers is a movable cart with a rack for boxes and a roof to provide shade. This cart is designed to be pushed along the outer edge of the small field where harvest is taking place.

This cart for field packing is designed to be pulled by a small tractor into the field when the crop is harvested. This type of cart can be used for field packing many types of crops. The roof folds down for easy transport, and opens up to provide a wide area of shade for the packers and the commodity. The cart design can be modified as needed to suit various products and different operations.

A self-propelled field pack system allows field workers to cut, trim, tie/wrap and pack in the field, thus eliminating the expense of operating a packing shed. In the illustration below, a fiat bed truck is moving along-side the field pack system, and packed produce is being loaded for transport.

SELF PROPELLED FIELD PACK SYSTEM

OPTIONS:

· Number of Worker positions per side. Row Spacing
· Ground Clearance
· Can Harvest front, rear, or both

Source: Highlander Ramsay Welding Machine Promotional Brochure. 1993.

Transport to the packinghouse

When crops are harvested at some distance from the packinghouse, the produce must be transported before packing. The gravity driven conveyor system for bananas illustrated below provides an example of how handling can be minimized during preparation for market. Harvested bananas are carried to the platforms set up along the conveyor route, then lifted and hung from hooks attached to the wire. Transport speed is controlled by workers who lead the produce to the packinghouse at the bottom of the hill.

Source: NIAE. 1977. Banana Conveyor. Tropical Agricultural Engineering Information O.D. Bulletin No. 7. National Institute of Agricultural Engineering, Silsoe, Bedfordshire, England. 15 pp.


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